Production of higher alkyl esters of inorganic acids



Patented Dec. 30, 1952 PRODUCTION OF HIGHER ALKYL ESTERS OF INORGANIC ACIDS Edouard A.

lands, assignor to M. F. Dahmen, Amsterdam, Nether- Shell Development Company,

San Francisco, Calif., a corporation of Delaware No'Drawing. Application June 26, 1950, Serial No. 170,481. In the Net 13 Claims. 1

This invention relates to the reaction of olefins of five or more carbon atoms per molecule with strong inorganic oxy-acids to produce the corresponding esters. It deals with an improved method for carrying out this reaction whereby increased yields of desirable products may be more efficiently obtained.

It is known that although the higher olefins react with inorganic oXy-acids, particularly the strong polybasic inorganic acids such as sulfuric acid, phosphoric acid and the like, to produce acid and neutral esters the process is more difiicult to carry out than is the case when olefins of less than five carbon atoms are used. This is due to the greater tendency of the higher olefins to form undesirable by-products under the reaction conditions. Thus, in addition to the desired esters, there is considerable formation of polymerization and condensation products when olefins of five or more carbon atoms are reacted with strong acids and, when sulfuric acid is used as the inorganic acid, alkyl sulfonic acids may be a further undesirable by-product. The extent of such by-product formation can be partially controlled by regulation of the reaction conditions such as the concentration of the acid used, the temperature and the reaction time. However, under the best conditions hitherto known the loss of olefin is still undesirably high.

It is an object of the present invention to provide an improved process of reacting olefins of five or more carbon atoms per molecule with strong inorganic oxy-acids whereby the foregoing disadvantages of prior methods are minimized or avoided. Another object isthe provision of a process whereby higher olefins may be more completely converted to esters of strong polybasic inorganic acids andalso higher yields of desirable esters may be obtained. Still another object of the invention is the more eflicient conversion of higher olefins to esters containing a high proportion of alkyl acid esters particularly useful for detergent manufacture. A further object is the provision of a process of esterifying higher olefins in which strong polybasic inorganic acids may be used at lower concentration than has previously been customary. Still other objects and advantages of the invention will be apparent from the following description of the new method of operation.

It has now been found that the reaction of olefins of five or more carbon atoms with strong inorganic oXy-acids is promoted'by the presence of a small amount of certain organic carbonyl herlands July 4, 1949 compounds, namely, those containing one or more aliphatic groups having five or more carbon atoms and which form oxonium compounds in a strongly acid medium. By carrying out the reaction in the presence of these promoters or accelerating substances the foregoing objects and other advantages are economically attained.

The invention is especially advantageous in the production of higher alkyl acid sulfates, in particular those of more than ten carbon atoms, preferably about 12 to 22 carbon atoms, per molecule which are especially suitable for conversion to secondary alkyl sulfuric acid ester salts which have superior surface-active properties making them exceptionally valuable for application as detergents, wetting agents, etc. Because of the special commercial importance of this application of the invention, it will be emphasized in the following discussion of the new method. However, as previously indicated, the invention is not limited to this preferred modification, but is equally applicable not only to the production of other sulfate esters of olefins of five or more carbon atoms but also to the manufacture of similar phosphoric acid esters and esters of other strong polybasic inorganic acids. In the sulfation of higher olefins to obain esters useful for conversion to surface-active alkyl sulfate salts, it is not only important to suppress undesirable side reactions, as previously pointed out, but also it is advantageous to proiote as much as possible the formation of monoalkyl sulfates. These yield the desired alkyl sulfate salts on neutralization with a base whereas any dialkyl sulfates which are formed require more exacting treatment. The dialkyl sulfates can be utilized for alkyl sulfate salt production by one or another of the methods described in U. S. Patent 2,139,393, for example, saponiflcation of the neutral esters by treatment with a base at elevated temperature to form the higher alkyl sulfate salt and higher alcohol. It is usually desirable, however, in the interest of economy to reduce the amount of dialkyl sulfate formed during sulfation of the olefins as much as possible in order to avoid treating any more neutral esters than is necessary. By reducing the concentration of the sulfuric acid used in sulfating higher olefins, polymerization and similar undesirable side reactions can be reduced to a certain extent, but there is a certain minimum limit for the concentration which varies according to the other sulfation conditions, and which usually lies above about for olefins with more than 10 carbon atoms. If a lower compound having an aliphatic or alicyclic group of at least five, preferably 6 to. 20, carbon atoms,v

the sulfation is much more complete and higher yields of sulfate esters are obtainedthan' is possible when operating under the same conditions of temperature, time of reaction, concentration of sulfuric acid and ratio of acid to olefin, but without the addition of a promoter for the reaction. Although the new process can thus be carried outwith advantage under the usual reaction conditions: for: sulfation, an important further advantageof the invention is that good yields of sulfuric acid alkyl esters can be obtained when using sulfuric acid of lower concentration than has heretofore been customary for theisulfaticn of olefins. Thus, for instance, by the'new method yields of mono-alkyl and dialkyl sulfates of 70% to 90% or even more can easily be obtained with sulfuric acid of about 92% to 95% or. even lower concentration under conditions which, in theabsence of the specified carbonylic promoters, give yields-of only a few per cent.

The possibility of working with sulfuric acid of'a lower concentration than usual, generally 2% to' 10% lower than the optimum in the absence of a carbonylic'promoter, not only has the advantage that the formation of polymerization products during the sulfation process is reduced, but also that when the excess sulfuric acid is recovered it does not have to be concentrated as'much in order to be suitable for re-use in the process.

It has further been found that the sulfuric acid esters obtained by the present process have a higher alkyl-2 sulfate content than the prod ucts'obtained by the, normal sulfation process. This is of great practical importance in view of thefact that the ester salts obtained from the 2-sulfates have better propertiesinter alia a better detergent effect and lesser hygroscopieity than the corresponding ester salts in which the sulfate group is situated nearer to the center'of the molecule.

The organic carbonyl compounds, which have a; promoting action in the-esterification of higher olefins with strong inorganic'oxy-acids andwhich are useful in the process of the invention, include, for example, the aliphatic ketones, aldehydes, carboxylic acids and carboxylic acid esters hav ing an aliphatic group of at least five carbon atoms. The promoter may contain. a plurality of" functional groups as in the keto-aldehydes, keto-acids, aldehydic acids, the esters of such acids or of keto cr 'aldehydic alcohols, etc. Other substituent groups or atoms, as hydroxyl groups or halogen. atoms, for example, may also be presentin the carbonyl compounds used as promoters or accelerators. Ithas been found that as a rule those promoters which have the carbonyl group in the terminal'position or near the end of an aliphatic chain are rather more active than the corresponding compounds having the-carbonyl groupsituated nearer the center of the molecule.

An especially active preferred group of promoters for use in the invention are the higher aliphatic lretones. Representative examples of promoters of this type which has been found to be useful are pentanone-Z, methyl isobutyl ketone, octanone-Z, dodecanone-Z and pentadecanone-2. Diacetone alcohol, mesityl oxide and isophorone are examples of other types of ketones which are effective promoters in the new process.

Likewise, very active as accelerating agents for the process are the higher aliphatic aldehydes such as heptanal, octanal, decanal and hexadecanal, for example. Unsaturated aldehydes which may be use include, for instance, tiglic aldehyde, citronellal, citral, and the like.

Another group of promoters which are very active is formed by the aliphatic monocarboxylic acids, especially those with more than six carbon atoms per molecule. Examples of promoters of this type which have been found to be suitable are octanoic acid, lauric acid, myristic acid, stearic acid and oleic acid. Esters of theseacids, including glycerides, glycol esters and monohydroxy alcohol esters, can likewise be used. Thus, methyl, ethyl, isopropyl and secondary and tertiary butyl esters of these acids are eifective promoters.

Among other esters which are promoters for the esterification of higher olefins with strong polybasic inorganic acids are, for instance, the formates, acetates, propionates, isobutyrates and valerates of alcohols of five or more carbon atoms per molecule such as heptanol-l, heptanol-2, heptanol-3, heptanol-, octanol-l, octanol-Z, nonanol-l, nonanol-Z, decanol-l, decanol-Z, dodecanol-l, docanol-2, pentadecanol-2, and stearyl alcohol. Most preferable esters of this type'are those of carboxylic acids of not more than three carbon atoms with primary or secondary alcohols of more than six carbon atoms. Suitable examples of these esters are, for instance, octyl-l acetate, octyl-2 acetate, tetradecyl-l acetate; etc. Keto esters which are affective are, for example, diacetone alcohol acetate, ethyl laevulinate and the like.

The carbonyl compounds used as promoters in the process of the invention can be added in the form of the pure or substantially pure individual compound, or as mixtures of two or more such compounds, or as mixtures of one or more such compounds with other substances which do not interfere with the olefin esterification. It is highly desirable, however, to avoid'the presence of compounds such as formaldehyde which give rise to the formation of dark-colored sulfation products.

Usually an addition of only a few per cent of the carbonyl compounds applied according to the invention, calculated on the olefins tobe esterified, brings about a considerable increase in the yield of inorganic acid esters. Additions of up to 10% are generally sufiicient, since no appreciable further increase in yield is as a rule achieved by the use of larger quantities.

The process according to the invention can be applied to the preparation of sulfuric acid or other. inorganic oxy-acid esters starting either with pure olefins or'with hydrocarbon mixtures containing olefins, such as the. products, or fractions thereof, obtained by cracking hydrocarbons. Products from cracking paraffin Wax or other paraffinic hydrocarbon material, and.

predominantly consisting of alpha-olefins, are

especially advantageous starting materials. Olefins of. 5 to 25 carbon atoms are preferred.

Although the process can be efiectedbatchwise or .intermittently, it is preferably carried out :in the continuous manner, the olefin, sulfuric or other strong polybasic inorganic acid and the carbonyl compound used as accelerating agent being passed in intimate contact with each other through a reaction space kept at the desired temperature; any unconverted portion of the olefin can then be recirculated. The accelerating agents may be removed from the esterification product, for example by extraction, before the latter is worked up further.

The conditions of reaction will vary with the particular inorganic oxy-acid and olefin or olefin mixture being used. With oxy-acids of sulfur such as sulfuric acid, pyrosulfuric acid, chlorosulfonic acid and the like, it is desirable to use low temperatures of the order of about C. to C. as a rule. The oxy-acids of phosphorus such as phosphoric and pyrophosphoric acids, for example, usually require higher temperatures of reaction but, as a general rule, temperatures of 50 C. or lower are preferred. The acid is preferably used at a concentration of between 85% and about 95% and may be used in amounts of 0.5 to 4 moles or more per mole of olefin treated. Short contact times of the order of about 5 to 50 seconds are most preferable as a rule, but, depending upon the type of reactor and the method of operation which are adopted, longer times, for example, about 5 to minutes or more, can be satisfactorily employed.

The examples below illustrate the beneficial effect achieved by using the carbonyl compounds of five or more carbon atoms according to the invention.

. Example I Pure dodecene-l, to which 5.8% by weight of oenanthal had been added, was brought into intimate contact with sulfuric acid of 95.0% in a film reactor of the type described in the Chemisch Weekblad, 37, 1940, pages 579-580. The molecular ratio of sulfuric acid to alkene was about 3, the temperature being kept at about 20 C. and the residence time of the mixture in the reactor being about 20 seconds. It was found from the analysis of the resulting sulfation product that the alkyl sulfuric acid yield was 45.5 mol per cent and the dialkyl sulfate yield was 35.9 mol per cent, corresponding to a total yield of 81.4 mol per cent.

When the reaction was carried out under the same reaction conditions but without the addition of oenanthal, the alkyl sulfuric acid and dialkyl sulfate yields amounted only to 5.3 and 0 mol per cent, respectively.

Similar results are obtained when using decanal, coconut oil glycerides or oleic acid in about the same amount in place of the oenanthal.

Example II Dodecene-l, to which 6.1% of pentadecanone-2 had been added, was sulfated under the same conditions as in Example I. Yields of alkyl sulfuric acid of 65.8 mol per cent and of dialkyl sulfate of 24.8 mol per cent were obtained, corresponding to a total yield of 90.6 mol per cent. The 2-sulfate content of the alkyl sulfuric acid was about 63%.

Similar results were obtained when the pentadecanone was replaced by an approximately equal quantity of decyl-l acetate, stearic acid or octanone-2.

Good results are also obtained when using 6 concentrated phosphoric acid as the inorganic acid instead of sulfuric acid.

"It will thus be seen that the invention offers many advantages over prior methods of esterifying higher olefins with strong polybasic inorganic acids. In addition to increasing the yield of esters and promoting the formation of more valuable alkyl-2 esters from olefins having the double bond near the end of the chain, the carbonyl compounds of five or more carbon atoms used in the new process exert a remarkable accelerating effect on the esterification reaction. The process is capable of wide variation not only in regard to the carbonyl compounds which may be used as promoters but also in respect to the olefins which may be esterified and the strong inorganic polybasic acids which may be employed as reactants. It will accordingly be understood that the invention is not restricted to the details of operation disclosed by way of illustration nor by any theory proposed in explanation of the improved results which are obtained.

I claim as my invention:

1. In a process of producing an ester of a strong polybasic inorganic acid of the group consisting of sulfuric acid, pyrosulfuric acid, phosphoric acid and pyrophosphoric acid by reacting said acid with an olefin having at least six carbon atoms per molecule, the improvement which comprises esterifying said olefin with said acid in the presence of an organic carbonyl compound having an aliphatic group containing at least five carbon atoms which is present in an amount not substantially greater than about 10% by weight of said olefin.

2. A process of producing an ester of a strong polybasic inorganic acid of the group consisting ofsulfuric acid, pyrosulfuric acid, phosphoric acid and. pyrophosphoric acid which comprises reacting an olefin having at least five carbon atoms per moleculewith a strong polybasic inorganic oXy-acid of the group consisting of sulfuric acid, pyrosulfuric acid, phosphoric acid and pyrophosphoric acid in the presence of about 1% to 10% by weight, based upon said olefin, of an aliphatic carbonyl compound having at least five carbon atoms per molecule.

3. A process of sulfating an olefin of 5 to 25 carbon atoms per molecule which comprises reacting said olefin with sulfuric acid in the presence of a small amount not substantially greater than about 10% by weight of said olefin of an aliphatic carbonyl compound having at least five carbon atoms per molecule.

4. A process of sulfating an olefin of 10 to 22 carbon atoms per molecule which comprises reacting said olefin with concentrated sulfuric acid in the presence of about 1% to about 10% by weight, based upon said olefin, of a ketone having an aliphatic chain of at least seven carbon atoms.

5. A process for producing an ester of a strong polybasic inorganic acid of the group consisting of sulfuric acid, pyrosulfuric acid, phosphoric acid and pyrophosphoric acid with an olefin of 5 to 25 carbon atoms per molecule which comprises reacting said olefin with a strong polybasic inorganic oxy-acid of the group consisting of sulfuric acid, pyrosulfuric acid, phosphoric acid and pyrophosphoric acid in the presence of about 1% to about 10% by weight, based upon said olefin, of a methyl-alkyl ketone of 7 to 25 carbon atoms per, molecule.

6. In a process of reacting an olefin of at least five carbon atoms per molecule with sulfuric acid 7 to produce an alkyl sulfate; the improvement which comprises adding to the reaction mixture a small amount not substantially greater than 10% by weight of said olefin of a saturated aliphatic carbonyl compound having '7 to 22 carbon atoms per molecule of the formula wherein R represents a member of the group consisting of hydrogen and alkyl radicals and R. represents an alkyl radical.

7. A process of sulfating an olefin of to 25 carbon atoms per molecule which comprises reacting said olefin with sulfuric acid in the presenceof a small amount not substantially greater than about by weight of said olefin of a saturated aliphatic aldehyde having '7 to carbon atoms per molecule. 8.- A process of sulfating an olefin of 5 to carbon atoms per molecule which comprises reacting said olefin with sulfuric acid in the presence of a small amount not substantially greater than about 10% by weight 01 said olefin of an aliphatic mono-carboxylic acid having 7 to 20 carbons atoms per molecule.

9. A process of sulfating an olefin of 5 to 25 carbon atoms per molecule which comprises reacting said olefin with sulfuric acid in the-presence of a small amount not substantially greater than about 10% by weight of said olefin of an aliphatic ester of a carboxylic acid which ester contains 7 to 22 carbon atoms per molecule.

10. A process of sulfating an olefin of 5 to 25 carbon atoms per molecule which comprises reacting said olefin with sulfuric acid in the pres-- ence of a small amount not substantially greater than about 10% by weight of said olefinof an ester of an aliphatic carboxylic acid of not more thanv 3 carbon atoms per moleculeand ansaliphatic alcohol having at least 5 carbon atoms per molecule.

11. A process of sulfating an olefinof 5 to 25 carbon atoms per molecule which comprises reacting said olefin with sulfuric acid in the presence of about 1% to about 10% by weight based upon said olefin of an ester of an aliphatic alcohol of not more than 3 carbon atoms perimolecule and an aliphatic carboxylic acid having at least 5 carbon atoms per molecule.

12. A process of sulfating an olefin in accordance with claim 3 wherein the reaction is carried out with sulfuric acid having a concentration between and about which is 2% to 10% lower than the optimum concentration for the sulfation under the reaction conditions in the absence of said carbonyl compound.

13. In a process of producing alkyl sulfate salts by sulfating a mixture of olefins of 12'to 18 carbon atoms predominating in terminally unsaturated olefins and neutralizing the alkyl acid sulfates produced with a base, the improvement which comprises carrying out said sulf'ation in the presence of a small amount not substantially greater than about 16% by weight of said olefin of an aliphatic carbonyl compound having at least 5 carbon atoms per molecule, whereby the formation of alkyl-2 sulfate esters is promoted.

EDOUARD A. M. F. DAHMEN.

REFERENCES CITED FOREIGN PATENTS Country Date Germany June 29, 1939 Number 

1. IN A PROCESS OF PRODUCING AN ESTER OF A STRONG POLYBASIC INORGANIC ACID OF THE GROUP CONSISTING OF SULFURIC ACID, PYROSULFURIC ACID, PHOSPHORIC ACID AND PYROPHOSPHORIC ACID BY REACTING SAID ACID WITH AN OLEFIN HAVING AT LEAST SIX CARBON ATOMS PER MOELCULE, THE IMPROVEMENT WHICH COMPRISES ESTERIFYING SAID OLEFIN WITH SAID ACID IN THE PRESENCE OF AN ORGANIC CARBONYL COMPOUND HAVING AN ALIPHATIC GROUP CONTAINING AT LEAST FIVE CARBON ATOMS WHICH IS PRESENT IN AN AMOUNT NOT SUBSTANTIALLY GREATER THAN ABOUT 10% BY WEIGHT OF SAID OLEFIN. 